How do lice spread? - briefly
Lice are transmitted mainly through direct head‑to‑head contact, which allows the insects to move from one scalp to another. Secondary pathways include sharing items such as hats, hairbrushes, or bedding that have recent contact with an infested person.
How do lice spread? - in detail
Lice propagate primarily through direct contact with an infested host. The head louse (Pediculus humanus capitis) moves from one scalp to another when hair brushes, combs, hats, helmets, or other headgear are shared. Close physical interaction, such as hugging or playing, also enables transfer because the insects cling firmly to hair shafts and can crawl onto a new person within seconds.
Secondary pathways involve indirect contact with contaminated objects. Items that retain hair fragments, such as pillows, bedding, upholstered furniture, and car seats, may harbor viable lice for several days. When an uninfested individual rests on these surfaces, nymphs or adult lice can attach to the hair. Clothing and scarves that have been in prolonged contact with an infested scalp can serve as temporary reservoirs, although the insects survive less long away from a host.
Environmental conditions affect survival outside a host. Lice require temperatures between 20 °C and 30 °C and a relative humidity of 40–70 % to remain active. In cooler, drier settings, they become inactive and die within 24–48 hours. Consequently, the risk of transmission from fomites diminishes rapidly after removal from a human head.
Key factors influencing spread include:
- Frequency of head-to-head interaction in schools, camps, or sports teams.
- Shared use of personal items that contact hair.
- Insufficient cleaning of bedding, towels, and upholstered surfaces.
- Delay in detecting and treating infestations, allowing the population to increase exponentially (each female can lay up to 100 eggs over her lifespan).
Effective control relies on prompt identification, thorough removal of lice and nits, and isolation of personal items for at least 48 hours. Washing clothing and bedding in hot water (≥ 60 °C) or sealing them in airtight bags for two days eliminates residual insects. Regular inspection of close contacts prevents re‑infestation and interrupts transmission cycles.